The cerebral cortex (cloak) is the most highly differentiated department nervous system, it is heterogeneous, consists of a huge number nerve cells. The total area of ​​the bark is about 1200 square centimeters, 2/3 of which lies in the depths of the furrows. In accordance with phylogenesis, ancient, old, middle, and new crust are distinguished (Fig. 26).

ANCIENT CORK (paleocortecx) includes an unstructured cortex around the anterior perforated substance: near-terminal gyrus, subcallosal field (located on the inside of the hemispheres under the knee and beak of the corpus callosum).

OLD CORK (archicortex), two-three-layered, located in the hippocampus and dentate gyrus.

The MIDDLE CORK (mesocortex) occupies the lower part of the insular lobe, the parahippocampal gyrus and the lower limbic region, its bark is not completely differentiated.

NEW CORK (neocortex) makes up 96% of the entire surface of the hemispheres. According to morphological features, 6 main layers are distinguished in it, however, the number of layers varies in different areas of the cortex.

Layers of the bark(Fig. 26):

1 - MOLECULAR. There are few cells, it consists mainly of horizontal fibers of ascending axons, including nonspecific afferents from the thalamus, and the branches of the apical (apical) dendrites of the 4th layer of the cortex end in this layer.

2 - OUTER GRAIN. It consists of stellate and small pyramidal cells, the axons of which end in layers 3, 5 and 6, i.e. participates in the connection of various layers of the cortex.

3 - EXTERIOR PYRAMIDS. This layer has two sublayers. External - consists of smaller cells that communicate with neighboring areas of the cortex, especially well developed in the visual cortex. The inner sublayer contains larger cells that are involved in the formation of commissural connections (connections between the two hemispheres).

4 - INTERNAL GRAIN. Includes cells granular, stellate and small pyramids. Their apical dendrites rise into the 1st layer of the cortex, and the basal (from the base of the cell) into the 6th layer of the cortex, i.e. participate in the implementation of intercortical communication.

5 - GANGLIOSIC. It is based on giant pyramids (Betz cells). Their apical dendrite extends to layer 1, the basal dendrites run parallel to the cortical surface, and the axons form projection pathways to the basal ganglia, brainstem, and spinal cord.

6 - POLYMORPHIC. It contains cells of various shapes, but mostly spindle-shaped. Their axons go up, but mostly down and form associative and projection pathways that pass into the white matter of the brain.

Cells of different layers of the cortex are combined into "modules" - structural and functional units. These are groups of neurons from 10-1000 cells that perform certain functions, "process" one or another type of information. The cells of this group are predominantly located perpendicular to the surface of the cortex and are often referred to as "column modules".

Rice. 26. The structure of the cerebral cortex

I. molecular
II. outer granular
III. external pyramidal
IV. internal granular
V. ganglionic (giant pyramids)
VI. polymorphic

Rice. 27 Left hippocampus

7. corpus callosum
8. roller
9. bird spur
10. hippocampus
11. fringe
12. Leg

Sulci Cerebri). Between the furrows are located various sizes of the gyrus of the large brain (lat. gyri cerebri) .

In each hemisphere, the following surfaces are distinguished:

These three surfaces of each hemisphere, passing one into another, form three edges. Upper edge (lat. margo superior) separates the upper lateral and medial surfaces. Inferolateral edge (lat. margo inferolateralis) separates the upper lateral surface from the lower. Inferomedial edge (lat. margo inferomedialis) is located between the lower and medial surfaces.

In each hemisphere, the most protruding places are distinguished: in front - the frontal pole (lat. polus frontalis), behind - occipital (lat. polus occipitalis), and on the side - temporal (lat. polus temporalis) .

The hemisphere is divided into five lobes. Four of them are adjacent to the corresponding bones of the cranial vault:

1. frontal lobe (lat. lobus frontalis)
2. parietal lobe (lat. lobus parietalis)
3. occipital lobe (lat. lobus occipitalis)
4. temporal lobe (lat. lobus temporalis)

Furrows and convolutions of the upper lateral surface

Frontal lobe - indicated in blue. Parietal lobe - marked in yellow. The temporal lobe is indicated in green. Occipital lobe - marked in pink.

frontal lobe

The frontal lobe is separated from the parietal by a deep central sulcus (lat. Sulcus centralis). It starts on the medial surface of the hemisphere, passes to its upper lateral surface, goes along it a little obliquely, from back to front, and usually does not reach the lateral sulcus of the brain.

Approximately parallel to the central sulcus is the precentral sulcus (lat. sulcus precentralis), which does not reach the upper edge of the hemisphere. The precentral sulcus borders the precentral gyrus in front (lat. gyrus precentralis) .

Upper and lower frontal furrows (lat. sulci frontales superior and inferior ) are directed forward from the precentral sulcus. They divide the frontal lobe into:

From the lateral furrow to the top, small furrows called branches depart. The most constant of them are ascending (lat. ramus ascendens) and front (lat. ramus anterior) branches. The upper posterior part of the furrow is called the posterior branch (lat. ramus posterior) .

The inferior frontal gyrus, within which the ascending and anterior branches pass, is divided by them into three parts:

parietal lobe

It lies behind the central sulcus, which separates it from the frontal sulcus. It is delimited from the temporal by the lateral sulcus of the brain, from the occipital by a part of the parietal-occipital sulcus (lat. sulcus parietooccipitalis) .

Between the ascending and posterior branches of the lateral sulcus of the brain is a section of the cortex, referred to as the fronto-parietal tegmentum (lat. operculum frontoparietalis). It includes the posterior part of the inferior frontal gyrus, the lower sections of the precentral and postcentral gyrus, as well as the lower section of the anterior part of the parietal lobe.

Occipital lobe

On the upper lateral surface, it has no boundaries separating it from the parietal and temporal lobes, with the exception of the upper part of the parietal-occipital sulcus, which is located on the medial surface of the hemisphere and separates the occipital lobe from the parietal.

The largest of the furrows is the transverse occipital furrow (lat. sulcus occipitalis transversus ). Sometimes it is a continuation of the posterior intraparietal sulcus and in the posterior section passes into an unstable semilunar sulcus (lat. sulcus lunatus) .

temporal lobe

Has the most pronounced boundaries. It distinguishes between a convex lateral surface and a concave lower one. The obtuse pole of the temporal lobe is turned forward and somewhat downward. The lateral sulcus of the cerebrum sharply delimits the temporal lobe from the frontal lobe.

Two furrows located on the upper lateral surface: upper (lat. sulcus temporalis superior) and lower (lat. sulcus temporalis inferior) the temporal sulci, following almost parallel to the lateral sulcus of the brain, divide the lobe into three temporal gyrus: superior, middle and inferior (lat. gyri temporales superior, medius et inferior ) .

Those parts of the temporal lobe that are directed towards the lateral sulcus of the brain are indented with short transverse temporal sulci (lat. sulci temporales transversi). Between these furrows lie 2-3 short transverse temporal gyri, associated with the gyri of the temporal lobe (lat. gyri temporales transversi) and an island.

Islet share (islet)

Lies at the bottom of the lateral fossa of the brain (lat. Fossa lateralis cerebri).

It is a three-sided pyramid, turned by its top - the pole of the island - anteriorly and outwards, towards the lateral groove. From the periphery, the islet is surrounded by the frontal, parietal and temporal lobes, which are involved in the formation of the walls of the lateral sulcus of the brain.

The base of the island is surrounded on three sides by a circular furrow of the island (lat. sulcus circularis insulae).

Its surface is cut by a deep central groove of the island (lat. sulcus centralis insulae). This furrow divides the islet into anterior and posterior parts.

On the surface there are a large number of small convolutions of the insula (lat. gyri insulae). The large anterior part consists of several short convolutions of the insula (lat. gyri breves insulae), back - one long gyrus (lat. gyrus longus insulae) .

Furrows and convolutions of the medial surface

The frontal, parietal, and occipital lobes emerge on the medial surface of the hemisphere.

The cingulate gyrus is limited from above by the cingulate groove (lat. Sulcus cinguli). In the latter, an anterior part is convex towards the frontal pole and a posterior part, which, following along the cingulate gyrus and not reaching its posterior part, rises to the upper edge of the cerebral hemisphere. The posterior end of the sulcus lies behind the upper end of the central sulcus. Between the precentral sulcus, the end of which is sometimes clearly visible at the upper edge of the medial surface of the hemisphere, and the end of the cingulate sulcus, there is a paracentral lobule (lat. lobulus paracentralis) .

Above the cingulate gyrus, in front of the subcallosal field, begins the medial frontal gyrus (lat. gyrus frontalis medialis). It stretches to the paracentral lobule and is the lower part of the superior frontal gyrus.

Behind the cingulate groove lies a small quadrangular lobule - the fore-wedge (lat. precuneus). Its posterior border is the deep parietal-occipital sulcus (lat. sulcus parietooccipitalis), lower - subtopic furrow (lat. sulcus subparietalis), which separates the precuneus from the posterior cingulate gyrus.

Behind and below the prewedge lies a triangular lobule - a wedge (lat. cuneus). The convex outer surface of the wedge participates in the formation of the occipital pole. The top of the wedge directed downward and forward almost reaches the posterior cingulate gyrus. The posterior lower border of the wedge is a very deep spur furrow (lat. sulcus calcarinus), anterior - parieto-occipital sulcus.

Furrows and convolutions of the lower surface

On the lower surface of the frontal lobe is the olfactory groove (lat. sulcus olfactorius). Inward from it, between it and the lower medial edge of the hemisphere, lies a straight gyrus (lat. gyrus rectus). Its posterior section reaches the anterior perforated substance (lat. substantia perforata anterior). Outside of the furrow is the rest of the lower surface of the frontal lobe, indented with short orbital furrows (lat. sulci orbitales), on a number of small orbital gyri (lat. gyri orbitales) .

The lower surface of the temporal lobe is a deep groove of the hippocampus (lat. sulcus hippocampi) is separated from the legs of the brain. In the depths of the furrow lies a narrow dentate gyrus (lat. gyrus dentatus). Its anterior end passes into the hook, and the posterior end into the tape gyrus (lat. gyrus fasciolaris) lying under the roller of the corpus callosum. Lateral to the sulcus is the parahippocampal gyrus (lat. gyrus parahippocampalis). Ahead, this gyrus has a thickening in the form of a hook (lat. uncus), and posteriorly continues into the lingual gyrus (lat. gyrus lingualis). The parahippocampal and lingual gyrus on the lateral side is limited by the collateral groove (lat. sulcus collateralis), passing anteriorly into the nasal groove (lat. sulcus rhinalis). The rest of the lower surface of the temporal lobe is occupied by the medial and lateral occipital-temporal gyrus (lat. gyri occipitotemporales medialis et lateralis ), separated by the occipital-temporal sulcus (lat. sulcus occipitotemporalis). The lateral occipital-temporal gyrus is separated from the inferior temporal gyrus by the inferolateral edge of the hemisphere.

Histology

Structure

Cytoarchitectonics (arrangement of cells)

• molecular layer
• outer granular layer
• layer of pyramidal neurons
• inner granular layer
• ganglion layer (inner pyramidal layer; Betz cells)
• layer of polymorphic cells

Myeloarchitectonics (fibre arrangement)

The cerebral cortex is represented by a layer of gray matter with an average thickness of about 3 mm (1.3 - 4.5 mm). It is most strongly developed in the anterior central gyrus. The abundance of furrows and convolutions significantly increases the area of ​​the gray matter of the brain. The cortex contains about 10-14 billion nerve cells. Its various sections, which differ from each other in some features of the location and structure of cells (cytoarchitectonics), the location of fibers (myeloarchitectonics) and functional significance, are called fields. They are places of higher analysis and synthesis of nerve impulses. There are no sharply defined boundaries between them. The cortex is characterized by the arrangement of cells and fibers in layers.

Cytoarchitectonics

Pyramidal cells of different layers of the cortex differ in size and have different functional significance. Small cells are intercalary neurons, the axons of which connect separate parts of the cortex of one hemisphere (associative neurons) or two hemispheres (commissural neurons). These cells are found in varying numbers in all layers of the cortex. The human cerebral cortex is especially rich in them. The axons of large pyramidal neurons take part in the formation of pyramidal pathways that project impulses to the corresponding centers of the brain stem and spinal cord.

The neurons of the cortex are located in unsharply demarcated layers. Each layer is characterized by the predominance of any one type of cell. There are 6 main layers in the motor cortex:

The cerebral cortex also contains a powerful neuroglial apparatus that performs trophic, protective, supporting and delimiting functions.

On the medial and lower surfaces of the hemispheres, sections of the old, ancient crust have been preserved, which have a two-layer and three-layer structure.

molecular layer

The molecular layer of the cortex contains a small number of small spindle-shaped associative cells. Their axons run parallel to the surface of the brain as part of the tangential plexus of nerve fibers of the molecular layer. The bulk of the fibers of this plexus is represented by branching of the dendrites of neurons of the underlying layers.

Outer granular layer

The outer granular layer is formed by small neurons with a diameter of about 10 microns, having a rounded, angular and pyramidal shape, and stellate neurons. The dendrites of these cells rise into the molecular layer. Axons either go into the white matter, or, forming arcs, also enter the tangential plexus of fibers of the molecular layer.

Layer of pyramidal neurons

It is the widest in comparison with other layers of the cerebral cortex. It is especially well developed in the precentral gyrus. The size of pyramidal cells consistently increases within 10-40 microns from the outer zone of this layer to the inner one. From the top of the pyramidal cell, the main dendrite departs, which is located in the molecular layer. Dendrites originating from the lateral surfaces of the pyramid and its base are of insignificant length and form synapses with adjacent cells of this layer. The axon of the pyramidal cell always departs from its base. In small cells, it remains within the cortex; the axon belonging to the large pyramid usually forms a myelinated associative or commissural fiber that goes into the white matter.

Inner granular layer

In some areas of the cortex, it is very strongly developed (for example, in the visual cortex). However, in other areas it may be absent (in the precentral gyrus). This layer is formed by small stellate neurons. It contains a large number of horizontal fibers.

Ganglion layer (Inner pyramidal layer; Betz cells)

It is formed by large pyramidal cells, and the region of the precentral gyrus contains giant cells, first described by the Kyiv anatomist V. A. Betz in 1874 (Betz cells). They reach a height of 120 and a width of 80 microns. Unlike other pyramidal cells of the cortex, giant Betz cells are characterized by the presence of large clumps of chromatophilic substance. Their axons form the main part of the cortico-spinal and cortico-nuclear tracts and terminate in the motor neurons of the brain stem and spinal cord.

Layer of multimorphic cells

It is formed by neurons of various, predominantly spindle-shaped shapes. The outer zone of this layer contains larger cells. The neurons of the inner zone are smaller and lie at a great distance from each other. The axons of the cells of the polymorphic layer go into the white matter as part of the efferent pathways of the brain. The dendrites reach the molecular layer of the cortex.

Myeloarchitectonics

Among the nerve fibers of the cerebral cortex, one can distinguish:

In addition to the tangential plexus of the molecular layer, at the level of the inner granular and ganglionic layers, there are two tangential layers of myelinated nerve fibers and axon collaterals of cortical cells. Entering into synaptic connections with the neurons of the cortex, horizontal fibers provide a wide distribution of the nerve impulse in it.

Module

I, II, III, IV, V, VI - layers of the bark
Afferent fibers
1. cortico-cortical fiber
2. thalamo-cortical fiber
2a. zone of distribution of specific thalamo-cortical fibers
3. pyramidal neurons
3a. inhibited pyramidal neurons
4. inhibitory neurons and their synapses
4a. cells with an axonal brush
4b. small basket cells
4c. large basket cells
4y. axoaxonal neurons
4d. cells with a double bouquet of dendrites (inhibitory inhibitory neurons)
5. spiny stellate cells, excitatory pyramidal neurons directly and by stimulating cells with a double bouquet of dendrites

Investigating the cerebral cortex, Sentagotai and representatives of his school found that its structural and functional unit is module- a vertical column with a diameter of about 300 µm. The module is organized around the cortico-cortical fiber, which is an axon of the pyramidal cell of the III layer (layer of pyramidal cells) of the same hemisphere (associative fiber), or from the opposite pyramidal cells (commissural). The module includes two thalamo-cortical fibers - specific afferent fibers that terminate in the IV layer of the cortex on spiny stellate neurons and extend from the base (basal) dendrites of pyramidal neurons. Each module, according to Sentagotai, is divided into two micromodules with a diameter of less than 100 microns. In total, there are approximately 3 million modules in the human neocortex. The axons of the pyramidal neurons of the module are projected to three modules of the same side and through the corpus callosum by means of commissural fibers to two modules of the opposite hemisphere. Unlike specific afferent fibers ending in layer IV of the cortex, cortico-cortical fibers form endings in all layers of the cortex, and, reaching layer I, give horizontal branches that go far beyond the module.

In addition to specific (thalamo-cortical) afferent fibers, spiny stellate neurons have an excitatory effect on output pyramidal neurons. There are two types of spiny cells:

The braking system of the module is represented by the following types of neurons:

System of inhibition of inhibitory neurons:

The powerful excitatory effect of focal spiny stellate cells is explained by the fact that they simultaneously excite pyramidal neurons and a cell with a double bouquet of dendrites. Thus, the first three inhibitory neurons inhibit pyramidal cells, and cells with a double bunch of dendrites excite them, inhibiting inhibitory neurons.

However, there are also critical and alternative concepts calling into question the modular organization of the cerebral cortex and cerebellum. Undoubtedly, these views were influenced by the prediction in 1985 and later by the discovery in 1992 of diffuse volumetric neurotransmitting.

Summary

The interneuronal interconnections of the neurons of the cerebral cortex can be represented as follows: incoming (afferent) information comes from the thalamus along the thalamo-cortical fibers, which end on the cells of the IV (inner granular) layer. Its stellate neurons have an excitatory effect on pyramidal cells III (pyramidal neurons) and V (ganglionic) layers, as well as cells with a double bunch of dendrites that block inhibitory neurons. The cells of layer III form fibers (associative and commissural) that connect the various sections of the cortex. Cells V and VI (multimorphic cells) of the layers form projection fibers that go into the white matter and carry information to other parts of the central nervous system. In all layers of the cortex there are inhibitory neurons that play the role of a filter by blocking pyramidal neurons.

The bark of various departments is characterized by the predominant development of one or another of its layers. Thus, in the motor centers of the cortex, for example, in the anterior central gyrus, layers III, V and VI are strongly developed and layers II and IV are poorly expressed. This so-called agranular type of cortex. Descending pathways of the central nervous system originate from these areas. In the sensitive cortical centers, where the afferent conductors coming from the organs of smell, hearing and vision end, the layers containing large and medium pyramidal cells are poorly developed, while the granular layers (II and IV) reach their maximum development. This granular type of bark .

Cytoarchitectonic Brodmann fields

Brodmann's cytoarchitectonic fields are sections of the cerebral cortex that differ in their cytoarchitectonics (structure at the cellular level). There are 52 Brodmann cytoarchitectonic fields.

Notes

1. M. G. Prives, N. K. Lysenkov, V. I. Bushkovich Human anatomy. - 11th. - St. Petersburg: "Hippocrates", 1998. - S. 525-530. - 704 p. - 5,000 copies. - ISBN 5-8232-0192-3
2. M. R. Sapin, Human Anatomy in 2 volumes - M .: Education, 1995. - ISBN 5-09-004385-X

The cerebral cortex , a layer of gray matter 1-5 mm thick, covering the cerebral hemispheres of mammals and humans. This part of the brain, which developed in the later stages of the evolution of the animal world, plays an extremely important role in the implementation of mental, or higher nervous activity, although this activity is the result of the work of the brain as a whole. Due to bilateral connections with the underlying parts of the nervous system, the cortex can participate in the regulation and coordination of all body functions. In humans, the cortex makes up an average of 44% of the volume of the entire hemisphere as a whole. Its surface reaches 1468-1670 cm2.

The structure of the bark . A characteristic feature of the structure of the cortex is the oriented, horizontal-vertical distribution of its constituent nerve cells in layers and columns; thus, the cortical structure is distinguished by a spatially ordered arrangement of functioning units and connections between them. The space between the bodies and processes of the nerve cells of the cortex is filled with neuroglia and the vascular network (capillaries). Cortical neurons are divided into 3 main types: pyramidal (80-90% of all cortical cells), stellate and fusiform. The main functional element of the cortex is the afferent-efferent (i.e., perceiving centripetal and sending centrifugal stimuli) long-axon pyramidal neuron. Stellar cells are distinguished by weak development of dendrites and powerful development of axons, which do not extend beyond the diameter of the cortex and cover groups of pyramidal cells with their branchings. Stellar cells act as receptive and synchronizing elements capable of coordinating (simultaneously inhibiting or exciting) spatially close groups of pyramidal neurons. A cortical neuron is characterized by a complex submicroscopic structure. Topographically different sections of the cortex differ in the density of the cells, their size, and other characteristics of the layered and columnar structure. All these indicators determine the architecture of the cortex, or its cytoarchitectonics. The largest divisions of the territory of the cortex are the ancient (paleocortex), old (archicortex), new (neocortex) and interstitial cortex. The surface of the new cortex in humans occupies 95.6%, the old 2.2%, the ancient 0.6%, the intermediate 1.6%.

If we imagine the cerebral cortex as a single cover (cloak) covering the surface of the hemispheres, then the main central part of it will be the new cortex, while the ancient, old and intermediate will take place on the periphery, i.e. along the edges of this cloak. The ancient cortex in humans and higher mammals consists of a single cell layer, indistinctly separated from the underlying subcortical nuclei; the old bark is completely separated from the latter and is represented by 2-3 layers; the new cortex consists, as a rule, of 6-7 layers of cells; intermediate formations - transitional structures between the fields of the old and new crust, as well as the ancient and new crust - from 4-5 layers of cells. The neocortex is subdivided into the following regions: precentral, postcentral, temporal, inferoparietal, superior parietal, temporoparietal-occipital, occipital, insular, and limbic. In turn, the areas are divided into sub-areas and fields. The main type of direct and feedback connections of the new cortex are vertical bundles of fibers that bring information from the subcortical structures to the cortex and send it from the cortex to the same subcortical formations. Along with vertical connections, there are intracortical - horizontal - bundles of associative fibers passing at various levels of the cortex and in the white matter under the cortex. Horizontal bundles are most characteristic of layers I and III of the cortex, and in some fields for layer V.

Horizontal bundles provide information exchange both between fields located on adjacent gyri and between distant areas of the cortex (for example, frontal and occipital).

Functional features of the cortex are determined by the distribution of nerve cells and their connections in layers and columns mentioned above. Convergence (convergence) of impulses from various sense organs is possible on cortical neurons. According to modern concepts, such a convergence of heterogeneous excitations is a neurophysiological mechanism of the integrative activity of the brain, i.e., analysis and synthesis of the body's response activity. It is also essential that the neurons are combined into complexes, apparently realizing the results of the convergence of excitations to individual neurons. One of the main morpho-functional units of the cortex is a complex called a column of cells, which passes through all cortical layers and consists of cells located on one perpendicular to the surface of the cortex. The cells in the column are closely interconnected and receive a common afferent branch from the subcortex. Each column of cells is responsible for the perception of predominantly one type of sensitivity. For example, if at the cortical end of the skin analyzer one of the columns reacts to touching the skin, then the other - to the movement of the limb in the joint. In the visual analyzer, the functions of perception of visual images are also distributed in columns. For example, one of the columns perceives the movement of an object in a horizontal plane, the neighboring one - in a vertical one, etc.

The second complex of cells of the new cortex - the layer - is oriented in the horizontal plane. It is believed that the small cell layers II and IV consist mainly of receptive elements and are "entrances" to the cortex. The large cell layer V is the exit from the cortex to the subcortex, and the middle cell layer III is associative, connecting various cortical zones.

The localization of functions in the cortex is characterized by dynamism due to the fact that, on the one hand, there are strictly localized and spatially delimited cortical zones associated with the perception of information from a particular sense organ, and on the other hand, the cortex is a single apparatus in which individual structures are closely connected and if necessary, they can be interchanged (the so-called plasticity of cortical functions). In addition, in every this moment cortical structures (neurons, fields, regions) can form coordinated complexes, the composition of which changes depending on specific and nonspecific stimuli that determine the distribution of inhibition and excitation in the cortex. Finally, there is a close interdependence between the functional state of the cortical zones and the activity of the subcortical structures. Territories of the crust differ sharply in their functions. Most of the ancient cortex is included in the olfactory analyzer system. The old and intermediate cortex, being closely related to the ancient cortex both by systems of connections and evolutionarily, are not directly related to the sense of smell. They are part of the system that controls the regulation of vegetative reactions and emotional states. New cortex - a set of final links of various perceiving (sensory) systems (cortical ends of analyzers).

It is customary to single out projection, or primary, and secondary, fields, as well as tertiary fields, or associative zones, in the zone of one or another analyzer. Primary fields receive information mediated through the smallest number of switches in the subcortex (in the optic tubercle, or thalamus, diencephalon). On these fields, the surface of peripheral receptors is, as it were, projected. In the light of modern data, projection zones cannot be considered as devices that perceive “point to point” irritations. In these zones, certain parameters of objects are perceived, i.e., images are created (integrated), since these parts of the brain respond to certain changes in objects, to their shape, orientation, speed of movement, etc.

Cortical structures play a primary role in the learning of animals and humans. However, the formation of some simple conditioned reflexes, mainly with internal organs, may be provided by subcortical mechanisms. These reflexes can also form at lower levels of development, when there is no cortex yet. Complex conditioned reflexes underlying integral behavioral acts require the preservation of cortical structures and the participation of not only the primary zones of the cortical ends of the analyzers, but also the associative - tertiary zones. Cortical structures are directly related to the mechanisms of memory. Electrical stimulation of certain areas of the cortex (for example, the temporal one) evokes complex pictures of memories in people.

Feature activity of the cortex - its spontaneous electrical activity, recorded in the form of an electroencephalogram (EEG). In general, the cortex and its neurons have rhythmic activity, which reflects the biochemical and biophysical processes taking place in them. This activity has a varied amplitude and frequency (from 1 to 60 Hz) and changes under the influence of various factors.

The rhythmic activity of the cortex is irregular, but several potentials can be distinguished by frequency. different types its (alpha, beta, delta and theta rhythms). The EEG undergoes characteristic changes in many physiological and pathological conditions(different phases of sleep, with tumors, convulsive seizures, etc.). The rhythm, i.e. frequency, and amplitude of the bioelectric potentials of the cortex are set by subcortical structures that synchronize the work of groups of cortical neurons, which creates the conditions for their coordinated discharges. This rhythm is associated with the apical (apical) dendrites of the pyramidal cells. The rhythmic activity of the cortex is superimposed by influences coming from the sense organs. So, a flash of light, a click or a touch on the skin causes the so-called. the primary response, consisting of a series of positive waves (the downward deflection of the electron beam on the oscilloscope screen) and a negative wave (the upward deflection of the beam). These waves reflect the activity of the structures of a given area of ​​the cortex and change in its various layers.

Phylogeny and ontogeny of the cortex . The bark is a product of long-term evolutionary development, during which the ancient bark first appears, arising in connection with the development of the olfactory analyzer in fish. With the release of animals from the water to land, the so-called. a cloak-like part of the cortex, completely separated from the subcortex, which consists of old and new cortex. The formation of these structures in the process of adaptation to the complex and diverse conditions of terrestrial existence is connected (by the improvement and interaction of various perceiving and motor systems. In amphibians, the cortex is represented by the ancient and the rudiment of the old cortex, in reptiles the ancient and old cortex are well developed and the rudiment of the new cortex appears. The greatest development the new cortex reaches in mammals, and among them in primates (monkeys and humans), proboscis (elephants) and cetaceans (dolphins, whales).Due to the uneven growth of individual structures of the new cortex, its surface becomes folded, covered with furrows and convolutions.Improvement of the cortex The telencephalon in mammals is inextricably linked with the evolution of all parts of the central nervous system.This process is accompanied by an intensive growth of direct and feedback connections connecting cortical and subcortical structures.Thus, at higher stages of evolution, the functions of subcortical formations begin to be controlled by cortical structures. This phenomenon is called corticolization of functions. As a result of corticolization, the brain stem forms a single complex with the cortical structures, and damage to the cortex at the higher stages of evolution leads to a violation of the vital functions of the body. Associative zones undergo the greatest changes and increase during the evolution of the neocortex, while the primary, sensory fields decrease in relative magnitude. The growth of the new cortex leads to the displacement of the old and ancient on the lower and median surfaces of the brain.

The cortical plate appears in the process of intrauterine development of a person relatively early - on the 2nd month. First of all, the lower layers of the cortex stand out (VI-VII), then the more highly located ones (V, IV, III and II;) By 6 months, the embryo already has all the cytoarchitectonic fields of the cortex characteristic of an adult. After birth, three critical stages can be distinguished in the growth of the cortex: at the 2-3rd month of life, at 2.5-3 years and at 7 years. By the last term, the cytoarchitectonics of the cortex is fully formed, although the bodies of neurons continue to increase up to 18 years. The cortical zones of the analyzers complete their development earlier, and the degree of their increase is less than that of the secondary and tertiary zones. There is a great diversity in the timing of maturation of cortical structures in different individuals, which coincides with the diversity of the timing of maturation of the functional features of the cortex. Thus, the individual (ontogeny) and historical (phylogenesis) development of the cortex is characterized by similar patterns.

On the topic : the structure of the cerebral cortex

Prepared

The cerebral cortex is represented by a uniform layer of gray matter 1.3-4.5 mm thick, consisting of more than 14 billion nerve cells. Due to the folding of the bark, its surface reaches large sizes - about 2200 cm 2.

The thickness of the cortex consists of six layers of cells, which are distinguished by special staining and examination under a microscope. The cells of the layers are different in shape and size. From them, processes extend into the depths of the brain.

It was found that different areas - fields of the cerebral cortex differ in structure and function. Such fields (also called zones, or centers) are distinguished from 50 to 200. There are no strict boundaries between the zones of the cerebral cortex. They constitute an apparatus that provides reception, processing of incoming signals and response to incoming signals.

In the posterior central gyrus, behind the central sulcus, is located zone of skin and joint-muscular sensitivity. Here, signals are perceived and analyzed that occur when touching our body, when it is exposed to cold or heat, or pain effects.

In contrast to this zone - in the anterior central gyrus, in front of the central sulcus, is located motor zone. It revealed areas that provide movement of the lower extremities, muscles of the trunk, arms, head. When this zone is irritated by an electric current, contractions of the corresponding muscle groups occur. Wounds or other damage to the cortex of the motor zone entail paralysis of the muscles of the body.

In the temporal lobe is auditory zone. Impulses arising in the receptors of the cochlea of ​​the inner ear are received here and analyzed here. Irritations of parts of the auditory zone cause sensations of sounds, and when they are affected by the disease, hearing is lost.

visual area located in the cortex of the occipital lobes of the hemispheres. When she gets irritated electric shock during brain surgery, a person experiences sensations of flashes of light and darkness. If it is affected by any disease, it worsens and vision is lost.

Near the lateral furrow is located taste zone, where the sensations of taste are analyzed and formed based on the signals that occur in the receptors of the tongue. Olfactory the zone is located in the so-called olfactory brain, at the base of the hemispheres. If these areas are irritated during surgical operations or when inflamed, people smell or taste certain substances.

Purely speech zone does not exist. It is represented in the cortex of the temporal lobe, the lower frontal gyrus on the left, and in areas of the parietal lobe. Their illnesses are accompanied by speech disorders.

First and second signal systems

The role of the cerebral cortex in the improvement of the first signaling system and the development of the second is invaluable. These concepts were developed by I.P. Pavlov. The signal system as a whole is understood as the totality of the processes of the nervous system that carry out the perception, processing of information and the body's response. It connects the body with the outside world.

First signal system

The first signal system determines the perception of sensory-specific images through the senses. It is the basis for the formation of conditioned reflexes. This system exists in both animals and humans.

In the higher nervous activity of man, a superstructure has developed in the form of a second signaling system. It is peculiar only to man and is manifested by verbal communication, speech, concepts. With the advent of this signal system, abstract thinking became possible, the generalization of the countless signals of the first signal system. According to I.P. Pavlov, words have turned into “signals of signals”.

Second signal system

The emergence of the second signaling system became possible due to the complex labor relations between people, since this system is a means of communication, collective labor. Verbal communication does not develop outside of society. The second signaling system gave rise to abstract (abstract) thinking, writing, reading, counting.

Words are also perceived by animals, but completely different from people. They perceive them as sounds, and not their semantic meaning, like people. Therefore, animals do not have a second signaling system. Both human signaling systems are interconnected. They organize human behavior in the broadest sense of the word. Moreover, the second changed the first signaling system, since the reactions of the first began to largely depend on social environment. A person has become able to control his unconditioned reflexes, instincts, i.e. first signal system.

Functions of the cerebral cortex

Acquaintance with the most important physiological functions of the cerebral cortex indicates its extraordinary importance in life. The cortex, together with the subcortical formations closest to it, is a department of the central nervous system of animals and humans.

The functions of the cerebral cortex are the implementation of complex reflex reactions that form the basis of the higher nervous activity (behavior) of a person. It is no coincidence that she received the greatest development from him. The exceptional properties of the cortex are consciousness (thinking, memory), the second signaling system (speech), high organization work and life in general.

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Formed by neurons, it is a layer of gray matter that covers the cerebral hemispheres. Its thickness is 1.5 - 4.5 mm, the area in an adult is 1700 - 2200 cm 2. Myelinated fibers that form the white matter of the telencephalon connect the cortex to the rest departments of the . Approximately 95 percent of the surface of the hemispheres is the neocortex, or neocortex, which is phylogenetically considered the latest formation of the brain. Archiocortex (old cortex) and paleocortex (ancient cortex) have a more primitive structure, they are characterized by a fuzzy division into layers (weak stratification).

The structure of the bark.

The neocortex is formed by six layers of cells: the molecular lamina, the outer granular lamina, the outer pyramidal lamina, the inner granular and pyramidal laminae, and the lamina multiforme. Each layer is distinguished by the presence of nerve cells of a certain size and shape.

The first layer is the molecular plate, which is formed by a small number of horizontally oriented cells. Contains branching dendrites of pyramidal neurons of the underlying layers.

The second layer is the outer granular plate, consisting of the bodies of stellate neurons and pyramidal cells. This also includes a network of thin nerve fibers.

The third layer - the outer pyramidal plate consists of the bodies of pyramidal neurons and processes that do not form long pathways.

The fourth layer - the inner granular plate is formed by densely spaced stellate neurons. They are adjacent to thalamocortical fibers. This layer includes bundles of myelin fibers.

The fifth layer - the inner pyramidal plate is formed mainly by large Betz pyramidal cells.

The sixth layer is a multiform plate, consisting of a large number of small polymorphic cells. This layer smoothly passes into the white matter of the cerebral hemispheres.

Furrows cortex each of the hemispheres is divided into four lobes.

The central sulcus begins on the inner surface, descends down the hemisphere and separates the frontal lobe from the parietal. The lateral groove originates from the lower surface of the hemisphere, rises obliquely to the top and ends in the middle of the upper lateral surface. The parietal-occipital sulcus is localized in the back of the hemisphere.

Frontal lobe.

The frontal lobe has the following structural elements: frontal pole, precentral gyrus, superior frontal gyrus, middle frontal gyrus, inferior frontal gyrus, operculum, triangular and orbital parts. The precentral gyrus is the center of all motor acts: from elementary functions to complex complex actions. The richer and more differentiated the action, the larger the zone occupied by the given center. Intellectual activity is controlled by the lateral divisions. The medial and orbital surfaces are responsible for emotional behavior and vegetative activity.

Parietal lobe.

Within its limits, the postcentral gyrus, intraparietal sulcus, paracentral lobule, superior and inferior parietal lobules, supramarginal and angular gyrus are distinguished. Somatic sensitive cortex is located in the postcentral gyrus, an essential feature of the location of functions here is the somatotopic dissection. The entire remaining parietal lobe is occupied by the associative cortex. It is responsible for the recognition of somatic sensitivity and its relationship with various forms of sensory information.

Occipital lobe.

It is the smallest in size and includes the lunate and spur sulci, the cingulate gyrus and the wedge-shaped area. Here is the cortical center of vision. Thanks to this, a person can perceive visual images, recognize and evaluate them.

The temporal share.

On the lateral surface, three temporal gyri can be distinguished: superior, middle, and inferior, as well as several transverse and two occipitotemporal gyri. Here, in addition, is the gyrus of the hippocampus, which is considered the center of taste and smell. The transverse temporal gyrus is a zone that controls auditory perception and interpretation of sounds.

limbic complex.

It unites a group of structures that are located in the marginal zone of the cerebral cortex and the visual mound of the diencephalon. It's limbic cortex, dentate gyrus, amygdala, septal complex, mastoid bodies, anterior nuclei, olfactory bulbs, bundles of connective myelin fibers. The main function of this complex is the control of emotions, behavior and stimuli, as well as memory functions.

The main violations of the functions of the cortex.

The main disorders to which cortex, divided into focal and diffuse. Of the focal, the most common are:

Aphasia - a disorder or complete loss of speech function;

Anomia - the inability to name various objects;

Dysarthria - articulation disorder;

Prosody - violation of the rhythm of speech and placement of stresses;

Apraxia - inability to perform habitual movements;

Agnosia - the loss of the ability to recognize objects with the help of sight or touch;

Amnesia is a memory impairment, which is expressed by a slight or complete inability to reproduce information received by a person in the past.

Diffuse disorders include: stunning, stupor, coma, delirium, and dementia.